The present invention is directed to pressure sensitive adhesive film material suitable for use, for example, as pressure sensitive adhesive tape and the like. In particular, the present invention is directed to pressure sensitive film material which causes substantially less fogging of adjacent surfaces, such as glass surfaces, due to outgassing of materials, such as plasticizers and the like.
Pressure sensitive adhesive tapes are well-known for use in diverse applications. Typically, PSA tapes employ a backing film or web, such as a plastic film, to carry a layer of pressure sensitive adhesive. Among the numerous use applications well-known for PSA tapes are electrical tape and harness tape, that is, tape used for securing bundles of wires in wire harness fabrication. Existing PSA tapes have various shortcomings, especially PSA tapes employing a flexible polyvinyl chloride (PVC) backing web. PVC materials are difficult to recycle, due in part to their halogen content, and due in part to poor stability during processing since Hydrochloric acid is a byproduct of the decomposition of this polymer. In addition, PVC films typically employ significant quantities of plasticizers to achieve adequate conformability and other performance characteristics. The plasticizer content of PVC film is problematic in many use applications, due in part to its outgassing over time, especially at elevated temperatures. Not only can such plasticizer outgassing degrade the properties of the PSA tape, this process also can result in fogging of adjacent surfaces. The outgassed plasticizer condenses on adjacent surfaces causing a fog or haze on the surface. Notably, PVC adhesive tapes employed in wiring harnesses used in the passenger compartment of motor vehicles, such as in the dashboard, are a significant cause of windshield fogging.
Notwithstanding these longstanding shortcomings, PSA tapes employing PVC backing films have not easily been replaced. Numerous performance characteristics must be met by any replacement PSA tapes. Particularly for use as harness tape, a PSA tape must demonstrate good use characteristics, such as good conformability, with stress relaxation and dead fold properties, as well as hand tearability. In addition, any such replacement PSA tape must have good long-term heat aging in view of the extended product life for a motor vehicle wire harness, and especially in view of the temperature cycling which occurs within a motor vehicle passenger compartment or, even more so, within a motor vehicle engine compartment. In addition, PSA tape intended for use as harness tape typically is supplied in rolls, and must unwind from the roll without ratcheting and without requiring excessive force since, frequently, they are applied by hand. Further, it is highly desirable that any such alternative to the known PVC tapes should have a laterally-across straight edge tear by hand. That is, a person applying the tape should be able to easily rip the tape from the remaining roll at 90 to the longitudinal direction of the tape with substantially no curl or jaggedness at the newly-formed free end of the tape. Similarly, the force required to cross-rip the tape by hand must not be excessive, yet the tape must exhibit strength adequate to its intended application. Of course, the tape must also have a suitable adhesiveness level. Thus, the backing film or web must be compatible with a suitable adhesive which when combined with the backing web provides the aforesaid performance characteristics. Compatibility of the adhesive and the backing web is required to ensure the integrity of the interfacial bond between the backing web and the adhesive, while avoiding problems such as xe2x80x9cblockingxe2x80x9d of the adhesive tape roll. Moreover, the backing web and the compatible adhesive desirably would be employed with existing, commercially known manufacturing equipment and techniques for producing PSA tape. Better PVC alternatives are needed for pressure-sensitive adhesive tapes and other PSA film materials, having performance characteristics meeting most or all of these industry criteria. Large end users of PSA tapes and other PSA film materials, such as the motor vehicle industry, have long desired new materials which demonstrate less fogging and yet meet the other stringent performance characteristics required of the particular use application. While innumerable polymer materials are known which might be formed into films or webs for use in adhesive tape applications, efforts to identify a suitable alternative to PVC films for pressure sensitive adhesive materials have encountered difficulties either in the performance of the film material itself, its compatibility with a suitable adhesive, or both.
It is an object of the present invention to provide flexible, conformable, pressure-sensitive adhesive film material which exhibits low or insignificant fogging. It is a particular object of at least certain preferred embodiments of the invention to provide PSA tape and other PSA film material suitable to serve as an alternative to known PVC adhesive tapes in diverse application including, for example, as harness tape for passenger compartment and engine compartment wire harnesses for motor vehicles and similar applications. Additional objects and advantages of the present invention will be more fully understood from the following disclosure and detailed description of the invention.
Selection and development efforts have now lead to a new class of pressure sensitive adhesive tapes and other flexible, conformable PSA film materials having excellent performance characteristics. The PSA film materials disclosed here do not require PVC backing films and, therefore, can achieve substantially reduced fogging. Various embodiments of the invention are suitable for use as electrical tapes, binding tapes, etc., and numerous use applications will be apparent to those skilled in the art given the benefit of the following disclosure and detailed description. Notably, certain preferred embodiments of the new PSA film materials disclosed here, that is, preferred versions employing certain advantageous combinations of materials, layer thicknesses, etc., are found to provide excellent performance characteristics for use as wire harness wrapping tape, especially as harness tape for motor vehicle passenger compartment and engine compartment applications.
In particular, pressure-sensitive adhesive film material disclosed here, as roll tape or in other forms, are found to have performance characteristics suitable for numerous applications presently served by PSA materials employing polyvinyl chloride backing films. The PSA tapes and other materials disclosed here, in particular, can be formulated to have excellent conformability, with good stress relaxation and dead fold properties, as well as good hand even after extended storage or exposure in a use application. They also have good temperature stability for meeting long-term heat aging requirements. Formulated for harness tape applications, the PSA tapes of the present invention have excellent cross-rip properties, including laterally-across straight edge tear by hand. In that regard, cross-rip forces for such preferred harness tape embodiments can meet specified ranges appropriate for hand application of the tape. Also, the unwind forces of such preferred harness tape embodiments can meet ranges specified for hand application of the tape, with little or no ratcheting or blocking of the tape rolls. These advantageous performance characteristics have been obtained by identifying the compatibility of suitable adhesives with suitable plastic backing films and other required ingredients or components. The PSA film materials of the invention do not require PVC backing films and, hence, can be more readily recycled. Moreover, harness wrap tape in accordance with numerous and preferred embodiments of the invention can be produced using manufacturing equipment and methods which are in current commercial use, thereby providing significant advantage over any other alternative to PVC which would require development and investment in new manufacturing equipment and methods.
In accordance with one aspect, pressure sensitive adhesive film material comprises, in combination, a flexible, conformable plastic film formulated of plastic film polymers and optionally comprising additives, and a pressure sensitive adhesive layer on at least one surface of the plastic film, which is compatible with the plastic film. The plastic film preferable is less than about 8 mils thick and xe2x80x9crollablexe2x80x9d, i.e., readily wound into rolls. The plastic film polymers include at least thermoplastic ethylene/styrene interpolymer in major part and a temperature modifier polymer which can also be referred to as a temperature/tensile modifier polymer, for increasing the thermal resistance of the plastic film and improving its tensile properties. More specifically, the temperature modifier polymer increases the thermal resistance of the plastic film above the level of thermal resistance which the thermoplastic ethylene/styrene interpolymer would achieve without the modifier polymer. It has been found that preferred embodiments of such pressure-sensitive adhesive film materials, especially prepared as harness tape, have good flexibility, conformability, flame-retardency sufficient to be self-extinguishing (per ASTM D-1000), and performance characteristics including at least the following: Fogging Number (per SAE J1756-94) of at least 60; long term heat aging (per Ford ES-XU5T-1A303-AA, section 6.1 and 6.3 of at least 3000 hr at 85xc2x0 C.; unwind force (from a roll of the film material per ASTM D-1000 Method A or comparable test method) of from 15 to 60 ounces/inch, more preferably 25 to 50 ounces/inch; and adhesion to steel (per ASTM D-1000) of 25 to 65 ounces/inch. In accordance with preferred embodiments, the temperature modifier polymer of the plastic film is thermoplastic polyolefin. Suitable thermoplastic polyolefins include, for example, low-density polyethylene, high-density polyethylene, polypropylene, and polypropylene-modified rubber. Polypropylene-modified rubber is most preferred in view of the excellent temperature stability it provides to the pressure-sensitive adhesive tape or other film material, for meeting long-term heat aging requirements and for its softness and contribution to the conformability of the tape. As discussed further below, the pressure-sensitive adhesive layer of the PSA materials disclosed here preferably comprises predominantly acrylic based, isoprene based, natural rubber based, or butyl based adhesive compatible with the plastic film.
In accordance with another aspect, flexible, conformable, pressure sensitive film material comprises, in combination, a flexible, conformable plastic film formulated as described above, along with a pressure sensitive adhesive on one side of the plastic film, which is compatible therewith, and a plastic barrier layer. In accordance with preferred embodiments, the plastic film is an extruded film and the plastic barrier layer is coextruded with the plastic film. The plastic barrier layer typically is coextruded at a second surface of the plastic film opposite the first surface carrying the adhesive. Preferably, the plastic barrier layer is formulated of plastic film polymers comprising at least polyolefins or other ethylene/styrene interpolymers in major part. Optionally, the plastic barrier layer further comprises various additives, as further discussed below.
As noted above, discovery of the compatibility of suitable PSA adhesives with halogen-free plastic film formulated as disclosed above, has now provided pressure sensitive adhesive film materials suitable for use as an alternative to PVC adhesive tapes in numerous applications, with less fogging, better recyclability, and good performance characteristics meeting the requirements of those use applications. Additional aspects and advantages of the present invention will be understood by those skilled in the art given the benefit of the foregoing disclosure and the following more detailed description of certain preferred embodiments.